


Skirting the Issue

by KimberlyLikesCherries



Series: The Path to Yellow [9]
Category: Undertale (Video Game)
Genre: (mentions of) healthy discussions about sex, Biting, Body Issues mentioned, Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Thighs, Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Nightmare bottoms, Sex, Skirts, cross dressing, date night gone steamy, discussion of safewords?, hell yeah, idk what happened this was supposed to be vanilla sex, no skirts were harmed in the making of this fanfic, squishy - Freeform, vaginal intercourse
Language: English
Status: Completed
Published: 2020-07-05
Updated: 2020-07-05
Packaged: 2021-03-05 01:02:28
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 1
Words: 1,802
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/25085860
Author URL: https://archiveofourown.org/users/KimberlyLikesCherries/pseuds/KimberlyLikesCherries
Summary: Sans discovered Nightmare pulls off skirts nicely.
Relationships: (mentions of) Dream/Sans (OC), Nightmare/Sans (OC), sans/sans
Series: The Path to Yellow [9]
Series URL: https://archiveofourown.org/series/1706509
Comments: 36
Kudos: 87





	Skirting the Issue

**Author's Note:**

  * For [xX_Wairwolf44_Xx](https://archiveofourown.org/users/xX_Wairwolf44_Xx/gifts).



> Wolf wanted Sans to be in the skirt and Nightmare doing the jumping, but apparently I can’t write Top Nightmare- instead you get Bottom Nightmare with masochist tendencies and a Sans who likes to leave his mark, but is deathly scared of hurting his lover in a not fun way.

“You can’t honestly want me to wear this?” Nightmare asked, holding the skirt up like one would hold a particularly disgusting rag.

“Actually, I do. Why, is there something wrong with it?”

He turned to the other skeleton, a playfully mocking retort ready to fly off his tongue, but froze.

“What?” Sans asked, lifting a hand to his elbow but pausing midway and quickly dropping his hand back to his side.

In all this time of knowing each other, not once had Nightmare ever seen Sans wear anything but long sleeves and sweatpants; and now he couldn’t help but stare, taking in the shock of cream shaded bones.

Neck vertebrae open to the air, clavicle only interrupted by the spaghetti straps draping off them, and a peak of spine and hip crests from between the thin tank top and skimpy skirt- Nightmare felt saliva quickly building up in his mouth and he forced himself to swallow, not wanting to be caught drooling. It wasn’t like they hadn’t messed around before, but Sans had never really just let him  _look_ ; his bones were so white, and smooth, and...

Nightmare glanced down at his own greyed hands- weak and brittle from self neglect- and touched the fine cracks webbing out from around his almost useless right socket.

...he wasn’t any of that. In fact, this form was just as useless as it was unsightly without his protective layer of negativity, and he had no idea why Sans would ever want or admire a single thing about it; and yet his mate, his dear, thoughtful mate-

“Hey,” Nightmare jumped, head snapping up to Sans’ looming form as a hand gently pulled his away from his damaged socket, “If you’re really that uncomfortable I won’t mind if you shift back. You don’t have to wear the skirt either.”

It was a lie, Nightmare could see it in the tension in his shoulders and slight shrink of his eyelights; and it reminded him that Sans was probably just as uncomfortable as he was, if not more. It was one thing Nightmare wished they didn’t share, and Sans’ had it at a level that was near phobic.

Let’s back track a bit here and explain some things; specifically, what the hell these two are up to.

Today is their scheduled “date night,” and Sans had made arrangements (read: scared everyone off) for the house to be empty for most of the day as the two spent some quality time together. Sans did this every Sunday while the twins took turns for every other Sunday. What happened during date night was usually a toss up, but apparently Sans wanted them to wear skirts and try to improve their body issues for an hour or two this time.

Now that you’re up to date, back to the story!

“No, I’ll wear it.” Nightmare decided, “Just...let me go change into this really quickly.”

Sans let go of his hand with a relieved smile and nod, “Don’t let me stop you, Babe.”

Nightmare smiled back and headed for the stairs to change. By the time he came back, Sans was standing in the kitchen surveying the land.

“I’m back.” Nightmare announced as he walked in, “How do I look?”

Sans glanced over with a happy smile- that immediately dropped as his lights landed on him.

The guardian’s hands twisted together with nerves, “Is- is it that bad?”

Sans didn’t respond, instead walking over and looking him over with an intense stare.

“...S-Sans...? Mmph!”

Suddenly Sans was all around him, guiding Nightmare quickly but carefully into a nearby counter as teeth and tongue clashed together unexpectedly. When his back hit the edge of a countertop, Sans hardly skipped a beat and picked him up so he sat just on the edge; hands stroking purple tinged ecto covered thighs that he’d summoned just for the hell of it.

It was all very unusually gentle, If somewhat fast, and Nightmare tired of it quickly.

“Y-you can, be rough with me,” Nightmare breathed out between kisses, “I won’t break.”

Sans pulled back a bit, lights blown wide and lidded as he stared down into Nightmare’s own, “Don’t tempt me, Nightmare; I’m in no mood to be teased.”

The smaller skeleton felt himself shiver, enjoying the uncharacteristic dominance.

“No teasing, I promise.” He said, pulling their hips together by his legs and muffling a whine as the fabric of their skirts rubbed against his sensitive pelvis and heated lips. Sans hissed quietly above him, and Nightmare moaned as his mate’s hand briefly tightened on his thighs, digging into the flesh of his summoned ecto.

“Don’t!” Sans warned darkly through clenched teeth and sockets, “Don’t. I-...I really want to bite you.”

“Then do it,” Nightmare said, tilting his head to the side invitingly, “Bite me, Mark me up, just- don’t hold back; don’t treat me like glass.”

Sans sockets widened, something hungry flashing in his lights; the smaller could almost hear the flip of a switch as his mate shot forward into the crook of Nightmare’s neck and-!

Hesitated.

“...Sans?” The guardian whispered, hands clenching tightly onto the back of the taller’s top as he braced himself for the worst.

“I-...” he could feel Sans hands begin to shake subtly, “I-...”

“What’s wrong?” Nightmare asked, “Why did you stop?”

Sans forehead thumped gently against his collar bone, “We-...we need a word; a safe word. Something for you to say if I get out of hand.”

Relief made him see stars.

“Heh! Mate,” Nightmare’s desperate hold around Sans’ shoulders became a hug, “I can beat you into the ground if I so wished; you have nothing to fear-“

“Please.” Sans interrupted, pulling back to meet his lights, “Just, humor me. Please.”

“...very well. Think of something that kills your libido.”

Sans cracked a smile, “Babe, I’m not sure that’s how this works-“ Nightmare gave him a sour look, “-okay, okay! Sauerkraut.”

“Sauerkraut?”

“Don’t ask. You?”

“Apples.” Nightmare said. Sans raised a brow, but otherwise didn’t comment on it; instead his shoulders melted from the sides of his skull and he more slowly returned to Nightmare’s shoulder, teeth chattering in restrained want.

The smaller expected him to just latch on without preamble, so it startled Nightmare a bit when something warm and wet gently lapped at his vertebrae. He inhaled sharply, and Sans froze, but when he didn’t do anything but tilt his head more for better access his mate was quick to start back up, a soft purr rumbling through his chest.

Nightmare couldn’t help a quiet whine as his mate’s hands drifted away from his thighs and up his skirt, fingers following the curve of his bare cheeks and pulling him closer; grinding their pelvises together as Sans mouthed at his neck, canines digging teasingly into the vertebrae like he wanted to carve lines into the brittle bone- and then he bit down.

“Aah-!” Nightmare arched into his mate’s chest, core clenching as his soul stuttered behind his ribs, “Sans!”

The guardian felt an embarrassing gush of slick rush out of him, drooling out of his pussy and following the curve of his behind to the fingers kneading his ecto; and that embarrassment only grew as Sans pulled back with a self satisfied smirk and slightly heavy breathing.

“That,” Sans murmured, “Was a very satisfying reaction.”

Nightmare blushed, his own breathing slightly labored, “S-shut up. Haven’t I been teased enough?”

A thrill ran up his spine as Sans face took on a considering frown. He looked around and, as if realizing just how exposed both were, grimaced in disdain. From one blink to the next, Nightmare found himself flopping onto the soft fabric of their shared bed; and then just as quickly had his legs hooked onto Sans’ shoulders as he ground his newly formed, skirt covered cock against the smaller’s puffy, sensitive lips- and briefly against his clit, his own skirt flipped up around his spine.

“Haa!” Nightmare’s hands shot out to clutch onto the pair holding his shaking legs in place, “Yes! Again, again!”

Sans obliged, dragging long, sensual strokes against excited magic and quickly soaking the fabric between them. Panting, he peeled their hands away from Nightmare’s thighs and entangled their fingers together, leaning forward and pressing their joined hands against the bed on either side of his mate’s flushed skull. From this angle his cock brushed more frequently against his little lover’s clit without the barrier of fabric, and Nightmare showed his appreciation by moaning just that littlest bit louder.

“Faster, please!” He begged, “I’m- I’m so-!”

What transpired next was, and Sans couldn’t stress this enough, a complete freak accident; though all Nightmare knew was that one moment that wonderfully hot cock was finally satisfying his clit’s itch, and then next that same cock- slick with a mix of precum and his own fluids- was thrusting it’s way viciously past his puffy libia and into his burning core, stretching his unprepared passage out with a wonderful burning sensation as the intrusion pierced into him and brushed something buried deeply inside him.

For a second both held their breath in shock, gazes locking as both realized just what happened; and then Nightmare’s lights were rolling up into his skull as his pussy fluttered and clenched it’s way into a powerful orgasm, back arching as he wailed out his pleasure.

When he came to Sans was holding onto him for dear life, face buried into Nightmare’s shoulder as he let out high pitched whines of distress.

“S-...sans?” He panted out. He tried to move a moment later, only for Sans to keen loudly and wrap his arms even tighter around his ribs.

“D-don’t!” He cried, “Don’t move, p-please!”

“Wha-what’s wrong?” And then Nightmare’s inner muscles unintentionally clenched down.

Sans  _ sobbed. _

“Nononono!” He whined. “Please, I- I’m gonna- gonna-!”

Slowly, Nightmare wrapped his exhausted arms around his mate’s neck vertebrae, “It’s okay, Sans. You can cum.”

“No, no I can’t!” He denied vehemently, “W-we haven’t talked about t-this at all and I-!” A ragged gasp, “-I’m ruining e-everything!”

“Shhh, no mate, no you’re not.” He soothed, “Calm down, Sans. It hurts, right? I don’t mind. You can do it; I’m giving you permission.”

Unfortunately his mate was stubborn and refused again (though Nightmare noted a distinct lack of safe word), so he took matters into his own hands.

In a move that he was rather impressed with himself for, as his limbs were all in a very spaghetti-like state, he wrapped his legs firmly around Sans spine and bounced. Once, twice-!

Heat bloomed in his core as Sans made a strangled sound and clamped his teeth down onto his collar bone, sending tired arousal up and down Nightmare’s spine as his love filled him.

Unnoticed, Nightmare’s eyelights shifted into delicate little hearts.

**Author's Note:**

> So, what you think bruh?


End file.
